: This is an application to study the impact of a cognitive-behavioral hostility-reducing intervention on autonomic control of the cardiovascular system. It is based on a research program which explores the relationships among physiological/behavioral characteristics such as anxiety, hostility, depression, and physical conditioning, the central and autonomic nervous systems and cardiovascular and respiratory systems. Considerable evidence, initially anecdotal and in the past several decades empirical, indicates that hostility and anger are risk factors for coronary artery disease (CAD). This risk applies not only to patients with CAD but also to healthy people. Evidence also indicates that hostility is associated with dysregulation of autonomic period variability (HPV), a noninvasive index of autonomic regulation of the heart. Moreover, convincing data demonstrate that low levels of heart period variability confer risk of recurrent myocardial infarction in patients with CAD and of cardiac morbidity and mortality in healthy subjects. Finally data demonstrate that cognitive behavioral treatment (CBT) of hostility and anger is effective in reducing these negative personality characteristics. Together, these bodies of data suggest 1) that a mechanism by which hostility promotes the development of CAD is through the ANS and 2) that a CBT intervention to reduce hostility may enhance autonomic control of the heart. In this study, healthy subjects with high levels of hostility, measured by standard questionnaires, and the interpersonal Hostility Assessment Technique, will be assigned randomly to a 12-week CBT intervention or a wait-list control condition. Subjects will be tested of 24-hour levels of HPV and short-term HPV responses to laboratory challenges prior to the intervention, immediately following the intervention, and at 6-month follow-up. The investigators will test the hypothesis that daytime/24 hour HPV will be increased by the CBT intervention and that the HPV fall in response to laboratory challenge, which in high hostile subjects is greater than that in controls, will be reduced.